Introduction:
In 1991, Detterline et al, discovered the presence of the human parasite N. fowleri in Spirit Lake. This discovery is noteworthy due to the fact that N. fowleri is not commonly found in northern habitats, outside of man-made artificially heated waters. The physical requirements and life-cycle of N. fowleri can indicate the probable blooming point in Spirit Lake and it's possible affects on the community. The eruption of Mt. St. Helens was the key factor to inducing the proper conditions for a N. fowleri bloom. The required temperature, water acidity, dissolved iron, dissolved O2, prey availability, and lack of competition, created by the eruption all fell into place in the aftermath.
Description of Spirit Lake:
Spirit Lake sits on an elevation 3198ft above sea level (Lee, 1996). It is within 5 miles of the blast crater of Mt. St. Helens, which caused it to receive the full impact when the enormous lateral blast occurred (Lee, 1996). Before the eruption the pristine lake was considered by scientists to be a typical oligotrophic lake, its solutes were dilute and it was enveloped by a Douglas fir (Pseudotsuga menziesii) forest (Lee, 1996; McKnight et al, 1988).
On the 18th of May 1980, Mt. St. Helens experienced a violent eruption. A massive lateral blast caused a debris avalanche, of which Spirit lake was in the direct path. The debris displaced the water of the lake creating a wave extending to 260 m above lake level and up the mountain sides that surrounded the northern portion of the lake (Lee, 1996). This wash over the slopes brought with it pyrolized trees and other plants, soil, and ash when it settled back down on to its bed, which was raised by approximately 197 feet by the influx of debris (Lee, 1996).
The waters that were once known for their clarity now had the little transparency because of the deposited pyrolized organics and partially degraded lignin molecules, mostly from the forest. These caused the most significant change in the chemistry of the lake waters (Lee, 1996). Spirit lake was wiped of macrolife-forms (Lee, 1996). This changed the trophic structures to a chemoorganotrophic and chemolithotrophic structure (Wissmar et al, 1982). The dilution of the dissolved organic material did not occur at first because the natural outlets of the lake were dammed by debris and there was no water flowing in because of the lack of water from higher up on the volcano, this created a closed system (McKnight et al, 1988; Lee, 1996). In 1984- 85, a tunnel was built to give the lake an outlet to North Fork Toutle River, once again opening the system (Lee, 1996). The snow melt-water, together with rain, returned the cycle of annual dilution after the spring of 1981 (McKnight et al, 1988).
In 1991 Detterline et al, showed the presence, at a statistically significant 0.02 P value, population density of N. fowleri at 1/500 ml, using contingency tables and Wilk's Lambda test (Detterline et al, 1991). N. fowleri was not known to have lived in Spirit Lake before the eruption, although there was no specific testing looking for it. How N. fowleri got to be in such high numbers in Spirit Lake is worth exploring, especially when the populations of other species were so devastated by the eruption and took many years or the intervention of man to come back.
Description of Naegleria fowleri:
Naegleria fowleri is a thermotolerant micropredator, limax type amoebae, that lives in soil and warm freshwater (Detterline et al, 1991). Other related thermotolerant amoeboflagellates are amoeboflagellates Naegleria gruberi, N. lovaniensis, and N. australiensis which is pathogenic to mice. N. fowleri can be an opportunist parasite, causing a very rare, but almost always fatal brain infection when it is forced (in the flagellated or trophozoites form) up into the nasal cavity of humans and some other mammals. (Centers for Disease Control and Prevention, 2012; John and Hoppe, 1990). The amoeba follows the olfactory nerve into the brain where it feeds, causing primary amebic meningoencephalitis (PAM) See diagram 1 (Centers for Disease Control and Prevention, 2012; John and Nussbaum, 1983). There is no cure for PAM although N. fowleri shows sensitivity to hyperbaric pressure, this method of treatment has not yet been tested (Detterline et al, 1991).
Diagram 1Naegleria fowleri has three stages, cysts , trophozoites , and flagellated forms , in its life cycle. The trophozoites replicate by promitosis (nuclear membrane remains intact) . N. fowleri is found in fresh water, soil, thermal discharges of power plants, heated swimming pools, hydrotherapy and medicinal pools, aquariums, and sewage. Trophozoites can turn into temporary non-feeding flagellated forms which usually revert back to the trophozoite stage. Trophozoites infect humans or animals by penetrating the nasal mucosa and migrating to the brain via the olfactory nervescausing primary amebic meningoencephalitis (PAM). N. fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue, while flagellated forms are occasionally found in CSF. Cysts are not seen in brain tissue.
(Centers for Disease Control and Prevention, 2012)

One of the most noteworthy cases of PAM that illustrates the hardiness of N. fowleri, is the epidemic of 16 deaths between 1962 and 1965 in Czechoslovakia (Tyndall et al, 1989). After seven deaths were traced back to a swimming pool, the pool was closed and cleaned. The pool was reopened and within days five people became ill with PAM and died (Tyndall et al, 1989). The answer to how this happened is reflected in the story of Spirit Lake and is directly related to the amoebas life-cycle and preferred environment.
As diagram 1 shows N. fowleri has multiple life stages, each stage helps the amoebae to live under different conditions. The encystment stage helps N. fowleri survive in harsh environments and giving them the ability to overwinter in freshwater or sediment (Detterline et al, 1991). This stage can only maintain life up to the point where the substrate's pH becomes less than 2.1 or greater than 9.5, over crowding, the temperature below 5 C or above 45C, prolonged starvation, desiccation, chlorination > 0.5 mg/L or salinity becomes > 3.5%, waste build up, exposure to metabolic products of bacteria, lack of oxygen (Detterline et al, 1991; Gupta and Das, 1999; Weik and John, 1977). The flagellated stage increases the mobility of the N. fowleri and increase it's ability in infect host organisms (John and Nussbaum, 1983).
In 1972 Griffin greatly expanded our knowledge of N. fowleri behavior. He proposed a hypothesis that has been supported by many other researchers, called flagellate-empty habitat hypothesis. It states that in a nondevistated, species rich environment, the occurrence of N. fowleri is one for every twenty thermotolerant amoebas, and 10,000 non-thermotolerant amoebas for every thermotolerant amoeba (Griffin, 1972). The competition keeps N. fowleri numbers low. Conversely when the environment is devoid of competition, as in the case of a volcanic eruption into a lake, or a chlorinated swimming pool the population increase exponentially (Detterline et al, 1991). This competitor and predator free environment is now seen to be the most important contributing factor to the presence of absence of N. fowleri when compared to other important factors such as, temperature, dissolved iron content, and species diversity, in suitable waterways (Detterline et al, 1991). The evidence for this hypothesis is so strong that Griffin, one of the leading experts, who has written multiple papers on N. fowleri bluntly stated N. fowleri is successful when competitors and predators are purged from the habitat (1972).
Temperature:
As discussed above the temperature tolerance for N. fowleri in the laboratory is between 5 and 45 C, wild N. fowleri have been recorded in water at temperatures of 35 to 41C (Detterline et al, 1991; Tyndall et al, 1989) Griffin reported that in one of his laboratory experiments they were even growing at 45C so the high end of the tolerance maybe incorrect (1972). Although temperature is important to this thermotolerant (sometimes referred to as thermophilic) amoeboflagellates it is not as important as having an empty habitat (Detterline et al, 1991).
Although there is no recording of the water temperature on the day of the eruption of Mt St. Helens, it is likely that the water exceeded the tolerance of any N. fowleri in Spirit Lake. The cysts in the soil were more likely to have survived, and a considerable amount of soil was washed into the lake when the water reentered the basin. The day after the eruption the temperature of the surface water was
32.7C well within the tolerance of N. fowleri (Lee, 1996). In October of 1980 the temperature was 12.2C which was considered to be back to the lakes pre-eruption norms, which is also well within tolerance (Lee, 1996). For a reference of the dates at which the various requirements were met see table 1.
pH levels:
When Weik and John were perfecting the procedure to grow N. fowleri in the laboratory they found that the medium's optimum pH was 5.5 to 6.5 for unagitated cultures. They hypothesised that this low pH preference was due to it's preferred substrate of amino acids (1977). In Spirit Lake the amount of dissolved ionized fulvic acids and hydrophilic acids, were 80-90% of the organic material (Wissmar et al, 1990). Immediately after the eruption, on the 30th of June, the pH was tested 6.21 which was a substantial decrease from the April pH of 7.35. The lake remained within of near N. fowleri's preffered pH zone from June 6th to July 28th staying between 6.0 and 6.8 for the duration. By 1981 the pH had gone back up to the pre-eruption average of 7.35 which is still with in the tolerance (if not the preference)(Lee, 1996).
Dissolved iron concentration:
Although iron concentration is thought to be one of the more significant factors to the growth of
N. fowleri there was no information found on the requirements. In the wild N. fowleri has been found living in 1,210 ug/L, with a mean of 480.ug/L to a stream in Yosemite Creek that contained high iron content.(Detterline et al, 1991) In early June of 1980 the dissolved iron concentrations was measured to be from 1,300 to 3,600 ug/L which may or may not be within the liveable range of N. fowleri (Lee, 1996).
Oxygen (O2) levels-
N. fowleri has many mitochondria, unlike other parasitic amoeba which have none (Weik and John, 1979). Weik and John suspect that N. fowleri's need for high O2 concentrations are these mitochondria (1977). Infact O2 concentrations are so important they were considered to be the limiting factor in the growth of N. fowleri in the laboratory 02 depletion (78% saturation) precedes stationary growth phase (1977). When Weik and John were designing the procedure of growth of N. fowleri they were using a medium with a low pH (as discussed above) they speculated that this acidic environment was interfering with ATP synthesis, therefore, the O2 consumption would go down as the pH rose (1979).
O2 levels were most likely the limiting factor Spirit Lake as well as in the laboratory. After the eruption the methane oxidation was a significant source of O2 depletion together with the microbial life in the lake. In June 1980 the total bacteria was 5x10^6, whereas the oxygen producing organisms with chlorophyl were minimal with the lake's chlorophyl a count at 0.3 ug/L^-1 (Wissmar et al, 1982). The primary source of O2 at the time was wind-driven on the surface of the lake which was helped by the fact that the surface area was 80% larger than before the eruption (Wissmar et al, 1982; Lee, 1996). In July of 1981 could have survive in the epilimnion of the lake with the concentration up to 5.4mg/L (Lee, 1996). The level of O2 would only rise from this point. This is the probable time of the beginning of the N. fowleri bloom, because at this stage all of it's requirements were met or exceeded. The populations most likely increased as it's limiting factor (O2) increased.
Prey source:
As all ready discussed there were vast quantities of bacteria in Spirit Lake after the eruption. The literature does not discuss which species are preyed upon in the wild. In labs they are nourished with Panmede liver digest and calf serum in Page's amoeba saline (Weik and John, 1977), the bacteria Escherichia coli (Griffin, 1972), and cyanobacteria (Xinyao et al, 2006). This is a wide range of diets which may indicate that N. fowleri is unlike other phagotrophic single celled eukaryotes, which are considered to be very selective consumers (Xinyao et al, 2006). This would be logical considering the wide range of locations N. fowleri lives and the fact that most of the places where it is found the are low species diversity indices (Detterline et al, 1991). One prey item used in the lab was shown to have been in Spirit Lake long before the proposed time of N. fowler bloom. In August of 1980 there were cyanobacteria populations at 2.6 x 105 cells/L (Lee, 1996).
Competition:
As stated earlier the presence or absence of competition is a primary factor in the growth of N. fowleri populations. N. fowleri has many advantages compared to it's competitors with is comes to primary succession. These advantages suit it best in events such as the eruption of Mt. St. Helens. The lack of competition induces N. fowleri to transform from the trophozoite to the motile flagellate, which increases it's ability to colonize further, leading to a bloom (Detterline et al, 1991). In August of 1982 there was an extensive study of the organisms in Spirit Lake, flagellates are mentioned but no specific species identified (Lee, 1996). At the time of the discovery of N. fowleri by Detterline et al, there were only two competing species found in Spirit Lake, N. lovaniensis and Acanthamoeba sp (1991). These competitor maybe the cause of the end of the bloom, but with no indication of when they were first sited there is no way to be sure.
Factor Date met or exceeded
Temperature 19 May 1980
pH 30 June 1980
dissolved Iron Concentration June 1980
Dissolved O2 July 1981
Prey August 1980
Competition 18 May 1980
Pathogen August 1983
Probable Bloom begging point July 1981
(Table 1) Spirit Lake, N. fowleri probable timeline. Dates are as specific as possible. Information for this table was taken from various sources given in the body of the paper.

Interaction with community:
Of course, as with all living things, N. fowleri interacts with the other species in it's community. It is not only a predator it is also prey. Declerck et al showed that the bacteria Legionella pneumophila which is also virulent in humans, uses N. fowleri and N. lovaniensis as a host (2005). In 1983 L pneumophila was found to be present in Spirit Lake. This maybe another contribute to the lower than bloom level population numbers of N. fowleri.
humans are not the only host for N. fowleri, house mice, guinea pigs , sheep, cotton rats, squirrels, and muskrats are also susceptible . Mammals that were found to be highly resistant were opossums, raccoons, and rabbits (John and Hoppe, 1990). John and Hoppe's experiment illustrated that rodents were considerably more at risk of infection, an area for future work would be to test the rodents in the area around Spirit Lake for N. fowleri antibodies (1990). In the laboratory mice have been shown to contract PAM from swimming in contaminated water, in a similar way to humans (John and Nussbaum, 1983). May amd John, showed 1983 that the parasite could be passed between mice, the exposed mice showed symptoms of infection after 28 days of the death of the originally infected mice (1983). These second host mice showed an increase in mean time to death, when compared to the first host mice (May amd John, 1983). This observation has interesting implications for the Spirit Lake community. Both the N. fowleri population in the lake and the rodent population on the shore should be monitored, especially in the event of another reduction in N. fowleri competitors.
With this information one can establish a rough time line for when different N. fowleri requirements were met following the eruption. This gives an indication of the probable time of the N. fowleri bloom in the lake and also factors that may have contributed to its population decline. The research also gives some possible ramifications to the presence of N. fowleri as a pioneer.